I've taken my Springfield Armory Range Officer .45 ACP out twice now and put a total of 450 rounds through it. I picked up the brass and as I was going through it and sorting it out I noticed what I think is unusual markings on the cases. I sorted all the Winchester brass with silver primers out as those were reloads and were shot by friends who were at the range with me that day. This is new Winchester white box ammo with brass primers so I'm sure that this was fired from my pistol.

Here is a pic of three mags worth of brass out of the bunch. All have similar markings. It kind of looks like a powder burn down one side of the case. Is this usual, an improper seal at the case mouth, stiff new brass not expanding enough??? Any ideas? This is a brand new pistol so it's definitely under warranty.